1. Field of the Invention
The present invention concerns an energy conservation method for use in a system including two devices interconnected by a data communication link. The two devices have a power supply of limited autonomy and comprise, for example, a portable mobile telephone and a portable microcomputer. The invention also concerns a portable mobile telephone of this kind.
2. Description of the Prior Art
Portable data processing and telecommunication electronic devices call for considerable effort in terms of energy conservation. These devices use batteries of limited capacity and all possible energy conservation techniques must be adopted to increase their battery life. These techniques include switching off the whole or part of a device during periods in which the device is wholly or partially inactive. In the case of a portable mobile telephone, for example, this entails selective deactivation of power supply circuits for the transceiver and external units (display screen, etc) and clock circuits timing digital circuits such as the input/output interface, the central processor unit (typically a microprocessor) and the baseband processing circuit. Although some clock and power supply circuits are deactivated, timers are activated in order to reactivate these clock and power supply circuits after a predetermined time-delay, in order to reactivate the digital circuits that they time or the analog circuits that they supply with power. In the case of a portable mobile telephone that is wholly on standby, for example, timers are activated which at predetermined intervals reactivate circuits that have to listen out for call request messages on the radio link.
Considered in isolation, each of these data processing or telecommunication electronic devices (mobile telephone, microcomputer, etc) has remarkable battery life characteristics as the result of optimum control of deactivation of the device as soon as there is no longer any benefit in it remaining active, i.e. putting the device on standby. However, is clear that the energy conservation function in each of the two devices is not fully optimized when a data communication link is set up between a portable mobile telephone and a portable microcomputer, for example. As used here, the expression "data communication link" is to be understood as having a wider meaning than a mere physical link conveying data, encompassing the concept of communicating software layers in the interconnected devices.
FIG. 1 shows a portable mobile telephone 1 and a portable microcomputer 2 connected by a data communication link provided by a physical medium A. The mobile telephone 1 typically includes a radio transceiver 11 comprising a modulator circuit, a baseband processor circuit and a frequency synthesizer, a control unit 12, and input-output interface circuits 13a, 13b, 13c and 13d each associated with a respective external unit such as a display 14, a buzzer 15 and a keyboard 16. The above circuits are supplied with power by a battery 17. The transceiver 11 sends and receives radio signals via an antenna 1a. The transceiver 11 is connected to a microphone 11a and an earpiece 11b. The control unit 12 controls the transceiver 11 via a bus. The control unit 12 is also connected to each of the input-output interface circuits 13a through 13d.
The portable microcomputer 2 includes a screen 20 and a keyboard 21 connected to a control unit 24 by respective interface circuits 22 and 23 and an interface circuit 25 also connected to the control unit 24. The microcomputer 2 further includes a battery 26 supplying power to each of its circuits.
FIG. 2 shows in more detail the control units 12 and 24 of the portable mobile telephone 1 and the portable microcomputer 2, respectively. Each of the control units 12, 24 includes a microprocessor or microcontroller 120, 240, an associated memory 121, 241, and an activity controller 122, 242. The microcprocessor 120, 240 is connected to the activity controller 122, 242 by an activity control bus Bca, Bca' and to the associated memory 121, 241 by a bus B1, B2. The bus B1, B2 also connects the microprocessor 120, 240 to the interface circuits 13a-13d, 25. The data communication link between the mobile telephone 1 and the microcomputer 2 is implemented by the following circuits: the microprocessor 120, the interface circuit 13d, the physical medium A, the interface circuit 25 and the microprocessor 240. Two ends of the physical medium A are coupled to respective first inputs/outputs of the interface circuits 13d and 25 and the interface circuits 13d and 25 have respective second inputs/outputs connected to the microprocessor 120 by the bus B1 and to the microprocessor 240 by the bus B2.
There follows a description of one example of a prior art mode of operation of the portable mobile telephone 1 and the portable microcomputer 2 interconnected by the data communication link provided by the physical medium A. Initially, when the mobile telephone 1 is switched on, all its circuits are supplied with power and activated for a duration at least equal to the time needed to log the mobile telephone in the cell in which it is currently located. Then, for maximum energy conservation in the mobile telephone 1, the microprocessor 120 cuts off the supply of electrical power to some analog circuits, such as the radio circuits in the transceiver 11, and deactivates the clocks timing some digital circuits, such as the baseband processor circuit or the control unit 12. To this end, the control unit 12 includes the activity controller 122 controlled by the microprocessor 120. The microprocessor 120 sends a message on the activity control bus Bca to an input of the controller 122. On receiving this message, and according to its contents, the controller places the mobile telephone 1 wholly or partly on standby. In particular, it deactivates some or all of the clock circuits producing clock signals SH1 timing the digital circuits and starts timers that reactivate the clock circuits that have been deactivated, after a predetermined time-delay. When the mobile telephone 1 is wholly on standby, only the circuit 122 remains active. In this case, in one prior art system, at a predetermined time of reception of a call request radio message that corresponds to the expiry of a time-delay, the circuit 122 produces a signal that activates clock and power supply circuits which supply power to the radio circuits and time the digital circuits in the transceiver 11 and the control unit 12, in order to enable reception of a call request radio message. If any such call request message concerns the mobile telephone 1, other circuits are activated by the microprocessor via the activity controller, such as the screen 14 and the buzzer 15. All the circuits activated in this way are put back on standby by the microprocessor 120 via the controller 122 as soon as possible, i.e. at the end of the call if the call request message is addressed to the mobile telephone 1 or immediately after the call request message is received if it is not addressed to the mobile telephone.
The control circuit in the microcomputer 2 can also apply energy conservation management techniques in respect of its circuits by deactivating the power supply to the screen, the microprocessor 240, etc by means of the circuits 240 through 243. It uses the activity controller 242 which selectively deactivates clock circuits producing clock signals SH2 timing the digital circuits.
If a data communication link between the mobile telephone 1 and the microcomputer 2 is established via the interface circuits 13d and 25 in the mobile telephone 1 and the microcomputer 2, respectively, in the prior art some circuits may no longer make any contribution to energy conservation in the system comprising the mobile telephone 1 and the microcomputer 2. Typically, the wired connection between the microcomputer 2 and the mobile telephone 1 via the medium A precedes a data communication link set-up phase. To set up the link between them, messages are exchanged between the microcomputer 2 and the mobile telephone 1. The data link set up then allows the mobile telephone 1 to transmit data to the microcomputer 2 and the microcomputer 2 to transmit data to the mobile telephone 1. The data is transmitted to or received from the mobile telephone network via the mobile telephone 1, for example. The data link set up between the mobile telephone 1 and the microcomputer 2 complies with the Open Systems Interconnect (OSI) recommendations of the ISO, for example. The respective microprocessors 120 and 240 in the control units 12 and 24 therefore manage a common protocol for the data link between the mobile telephone 1 and the microcomputer 2. In the prior art protocols of this kind provide data link set-up and, maintain and clear-down phases, without solving the problem of energy expenditure resulting from the existence of the link. As shown by the shaded parts of FIG. 2, the circuits required for the link to exist, including the two microprocessors 120 and 240 and the interfaces 13d and 25 in the mobile telephone 1 and the microcomputer 2, respectively, are not put on standby or deactivated. This is because a data link enables only exchange of digital data, typically in the form of messages (frames, packets, etc), between the microcomputer 2 and the mobile telephone 1. This digital data does not allow remote activation of the interface circuits 13d, 25 and the microprocessors 120, 240 of one device by another, specifically in the case where the circuits 13d, 25 and 120, 240 of the remote device are on standby. The PHYSICAL layer of the data link is transparent to the data transmitted. It therefore cannot activate circuits involved in a data link on the basis of information received. In an application involving a mobile telephone connected to a microcomputer, each of these devices must be able to reactivate remotely circuits of the other device that are involved in the data link, failing which these circuits cannot be put on standby. For example, the mobile telephone must be able to reactivate the microcomputer in order to retransmit to it data that the mobile telephone has received.